Comparison of phosphate rock and triple superphosphate on a phosphorus-deficient Kenyan soil
1999
Mutuo, P.K. | Smithson, P.C. | Buresh, R.J. | Okalebo, R.J.
Soil phosphorus (P) deficiency is a constraint to crop production in many regions of sub-Saharan Africa, which could be overcome through use of either soluble P fertilizer or sufficiently reactive phosphate rock (PR). A field study was conducted with corn (Zea mays L.) for three growing seasons (18 months) on a P-deficient, acid soil in Kenya to compare a soluble P source (triple superphosphate, TSP) and relatively reactive Minjingu PR from Tanzania. In the 18 months following application of 250 kg P ha(-1), bicarbonate extractable inorganic soil P (P(i)) was higher for application of TSP than PR, but Pi extracted with a mixed anion-cation resin was comparable for TSP and PR. Inorganic P extracted by 0.1M NaOH, without prior extraction of resin and bicarbonate P(i), decreased during the 18 months following TSP application, but increased following PR application. After 18 months, about 7% of the added PR-P remained as Ca-bound P that was extracted with 1M HCl. The 1M HCl extractable P(i), however, underestimated residual PR-P that gradually dissolved and supplied plant-available P, as indicated by recovery of < 40% of PR-P added to soil in laboratory incubations even though PR solubility in HCl was > 90%. Minjingu PR was an effective source of P for corn. Corn yields were comparable for TSP and PR, and the relative agronomic effectiveness of PR averaged 107% in Season 1 and 79% in Season 3. Anion resin and mixed anion-cation resin appeared to be superior to bicarbonate and NaOH as a soil P test for use with both TSP- and PR-treated soils.
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